1. Field of the Invention
The present invention relates to a method and apparatus for processing waste gas exhausted from chemical vapor deposition (CVD) equipment whereby a dust and/or viscous substances are separated and removed from the waste gas exhausted from the CVD equipment.
2. Description of the Prior Art
CVD is one of the semiconductor processing techniques used to form a thin film. In the CVD technique, one or more compounds such as halides, sulfides, or hydrides or other simple gases containing the elements for comprising the thin film to be formed are supplied onto a substrate so that the desired thin film is deposited on the substrate by means of a chemical reaction (such as thermal decomposition, oxidation, reduction, polymerization, vapor phase reaction, etc. at a high temperature) occurring in a vapor phase or on the surface of the substrate. As the CVD technique is based on a chemical reaction, it is possible to form a thin film of a wide variety of elements. It is also possible to obtain an arbitrary composition by properly selecting the combination of materials used for the vapor phase reaction. Therefore, the CVD technique can be used to synthesize a film having an entirely new structure and/or composition which has not been known conventionally. The CVD technique has a further advantage that a thin film can be formed at a temperature much lower than the melting point of the film material.
For example, the CVD technique is used to form a SiO.sub.2 film on a Si substrate or the like by supplying a raw material such as SiH.sub.4 (mono-silane) or tetraethoxysilane (TEOS) onto the substrate. The CVD equipment exhausts waste gas that includes not only the unreacted gas which made no contribution to the formation of the film but also dust, such as particles of SiO.sub.2, and by-products of the film formation process such as alcohol, aldehyde, and highly viscous polysiloxane, etc. Many of these components in the waste gas are hazardous and therefore, it is prohibited to directly release the waste gas into the atmosphere so as to protect humans and the environment from any negative effects.
There are various known techniques for processing the waste gas exhausted from CVD equipment. For example Japanese Patent Laid-Open No. 5-261232 discloses as a wet-type apparatus, a scrubber for processing the waste gas exhausted from atmospheric-pressure CVD equipment which is adapted to spray cleaning water containing an anionic surface-active agent or nonionic surface-active agent through a shower nozzle of the scrubber.
Japanese Patent Laid-Open No. 3-229609 discloses a dry-type apparatus for processing the waste gas exhausted from CVD equipment in such a manner that the solid components contained in the waste gas exhausted from the CVD equipment are collected in the form of particles and disposed of, wherein the waste gas is cooled without using a water shower so that the particles are deposited on the surface of a plurality of layers of wire mesh provided in an exhaust path of the waste gas, and the particles are sucked up and disposed of by a vacuum cleaner.
However, in the wet technique disclosed in Japanese Patent Laid-Open No. 5-261232, the apparatus produces waste containing dust and highly toxic gas, and thus an after-treatment is required. In the example disclosed in Japanese Patent Laid-Open No. 3-229609, the technique requires an apparatus for cooling the waste gas at a rate of 4 to 5 m.sup.3 /min for each piece of CVD equipment so that the solid particles are changed into a powder form. For example, when waste gas containing a great amount of dust and highly-viscous substances such as polysiloxane produced during an atmospheric-pressure CVD process is collected and recovered, the highly-viscous substances are deposited on the surface of the wire mesh, and it is very difficult to remove the deposited highly-viscous substances by means of suction using a vacuum cleaner. Furthermore, the highly-viscous substances also deposit on the inner wall of the pipe connected to the vacuum cleaner, which leads to a reduction in its suction capabilities. Therefore, this technique cannot provide high efficiency in waste gas processing.
It is therefore an object of the present invention to provide a method and apparatus for processing waste gas exhausted from CVD equipment which overcomes the above described problems.